U.S. patent application number 13/082643 was filed with the patent office on 2012-10-11 for low cost fast charger with internal accumulator and method.
Invention is credited to Stuart M. Davis.
Application Number | 20120256583 13/082643 |
Document ID | / |
Family ID | 45932579 |
Filed Date | 2012-10-11 |
United States Patent
Application |
20120256583 |
Kind Code |
A1 |
Davis; Stuart M. |
October 11, 2012 |
Low Cost Fast Charger with Internal Accumulator and Method
Abstract
Disclosed is a charger device configured to charge a
rechargeable battery comprising at least one rechargeable
electrochemical cell includes a lead-acid battery charge
accumulator device of a high discharge rate, having a discharge
rate that is capable of delivering charging current to the at least
one rechargeable electrochemical cell to charge the at least one
rechargeable electrochemical cell within a period of about 5 to 15
minutes, a low rate 200 ma charger coupled in shunt with the
lead-acid battery high discharge rate charge accumulator device and
with the charger configured to re-charge the high discharge rate
charge accumulator at a low charge rate, in comparison to the
discharge rate of high discharge rate charge accumulator and a
series resistor coupled between the accumulator and an output of
the charger device.
Inventors: |
Davis; Stuart M.; (Norfolk,
MA) |
Family ID: |
45932579 |
Appl. No.: |
13/082643 |
Filed: |
April 8, 2011 |
Current U.S.
Class: |
320/103 ;
320/107; 320/155 |
Current CPC
Class: |
H02J 7/00302 20200101;
H02J 7/345 20130101; H02J 7/0029 20130101; H02J 7/00306 20200101;
H02J 7/342 20200101; H02J 7/00304 20200101 |
Class at
Publication: |
320/103 ;
320/155; 320/107 |
International
Class: |
H02J 7/04 20060101
H02J007/04; H02J 7/00 20060101 H02J007/00 |
Claims
1. A method for charging a rechargeable battery comprising at least
one rechargeable electrochemical cell, the method comprising:
charging the rechargeable battery at a high rate from a charge
accumulator device that has a discharge rate that is capable of
delivering charging current to the rechargeable electrochemical
battery to charge the rechargeable electrochemical cell within a
period of about 5 to 15 minutes; and recharging the charge
accumulator using a low charge rate charger, with the charge rate
to recharge the charge accumulator being low in comparison to the
charging rate of the rechargeable battery.
2. The method of claim 1 wherein the charge accumulator is a
lead-acid battery.
3. The method of claim 2 wherein the charge accumulator reaches an
approximately 13% depth of discharge for a single charge of the
rechargeable battery.
4. The method of claim 1 wherein low rate charger is a 200 ma.
charger.
5. The method of claim 1 wherein the charge accumulator is a
supercapacitor.
6. A charger device configured to charge a rechargeable battery
comprising at least one rechargeable electrochemical cell, the
device comprising: a charge accumulator device that has a discharge
rate that is capable of delivering charging current to the at least
one rechargeable electrochemical cell to charge the at least one
rechargeable electrochemical cell within a period of about 5 to 15
minutes; and a low charge rate charger configured to re-charge the
charge accumulator at a low charge rate, in comparison to the
charge rate of the electrochemical cell.
7. The charger device of claim 6 wherein the charge accumulator is
a lead-acid battery.
8. The charger device of claim 6 wherein the charge accumulator
reaches approximately 13% depth of discharge for a single charge of
the rechargeable cell.
9. The charger device of claim 6 wherein the low rate charger is a
200 ma charger.
10. The charger device of claim 6 further comprising: protection
circuitry coupled to the high discharge rate accumulator.
11. The charger device of claim 10 wherein the protection circuitry
comprises: a resistor coupled in series between the accumulator and
an output of the charger.
12. The charger device of claim 6 wherein the accumulator is
coupled in shunt with the low rate charger and output terminals of
the charger device.
13. The charger device of claim 11 wherein the accumulator is
coupled in shunt with the low rate charger, and the resistor and
output terminals of the charger device.
14. A charger device configured to charge a rechargeable battery
comprising at least one rechargeable electrochemical cell, the
device comprising: a lead-acid battery that has a high discharge
rate to provide a charge accumulator device that has a discharge
rate that is capable of delivering charging current to the at least
one rechargeable electrochemical cell to charge the at least one
rechargeable electrochemical cell within a period of about 5 to 15
minutes; and a low rate 200 ma charger coupled in shunt with the
lead-acid battery high discharge rate charge accumulator device and
with the charger configured to re-charge the high discharge rate
charge accumulator at a low charge rate, in comparison to the
discharge rate of high discharge rate charge accumulator; and a
series resistor coupled between the accumulator and an output of
the charger device.
Description
BACKGROUND
[0001] LiFePO.sub.4 batteries deliver high power and can be
recharged quickly at very high rates. However, in order to sustain
the high power levels required for rapid charging, a charger for
such batteries is typically larger and more expensive than a
conventional charger for batteries that charge at lower charge
rates. This attendant cost is due to the cost of larger/higher
performance components needed in such battery chargers to fast
charge LiFePO.sub.4 batteries.
SUMMARY
[0002] According to an aspect of the present invention, a method
for charging a rechargeable battery that includes at least one
rechargeable electrochemical cell is disclosed. The method includes
charging the rechargeable battery at a high rate from a charge
accumulator device that has a discharge rate that is capable of
delivering charging current to the rechargeable electrochemical
battery to charge the rechargeable electrochemical cell within a
period of about 5 to 15 minutes; and recharging the charge
accumulator using a low charge rate charger, with the charge rate
to recharge the charge accumulator being low in comparison to the
charging rate of the rechargeable battery.
[0003] Embodiments may include one or more of the following.
[0004] The charge accumulator is a lead-acid battery. The charge
accumulator reaches an approximately 13% depth of discharge for a
single charge of the rechargeable battery. The low rate charger is
a 200 ma. charger. The charge accumulator is a supercapacitor.
[0005] In other embodiments, the charge accumulator is a
rechargeable Ni--MH battery. Ni--Cd battery, Ni--Zn battery, Ni--Fe
battery, Ag.sub.2O--Zn battery, AgO--Zn battery, Ag.sub.2O--Cd
battery, AgO--Cd battery, Ag.sub.2O--MH battery, AgO--MH battery or
a high rate Lithium rechargeable battery such as Li--FePO.sub.4.
The charge accumulator may be physically larger and be rated to
contain substantially higher energy (W-hr) than the rechargeable
battery it is intended to recharge, to assure that the charge
accumulator is capable of recharging the rechargeable battery at a
very high rate.
[0006] According to an additional aspect of the present invention,
a charger device configured to charge a rechargeable battery
comprising at least one rechargeable electrochemical cell, the
device includes a charge accumulator device that has a discharge
rate that is capable of delivering charging current to the at least
one rechargeable electrochemical cell to charge the at least one
rechargeable electrochemical cell within a period of about 5 to 15
minutes; and a low charge rate charger configured to re-charge the
charge accumulator at a low charge rate, in comparison to the
charge rate of the electrochemical cell.
[0007] Embodiments may include one or more of the following.
[0008] The charge accumulator is a lead-acid battery. The charge
accumulator reaches approximately 13% depth of discharge for a
single charge of the rechargeable cell. The low rate charger is a
200 ma charger. The charger device further includes protection
circuitry coupled to the high discharge rate accumulator. The
protection circuitry comprises a resistor coupled in series between
the accumulator and an output of the charger. The accumulator is
coupled in shunt with the low rate charger and output terminals of
the charger device. The accumulator is coupled in shunt with the
low rate charger, and the resistor and output terminals of the
charger device.
[0009] According to an additional aspect of the present invention,
a charger device configured to charge a rechargeable battery
comprising at least one rechargeable electrochemical cell includes
a lead-acid battery or other high discharge rate charge accumulator
device having a discharge rate that is capable of delivering
charging current to the at least one rechargeable electrochemical
cell to charge the at least one rechargeable electrochemical cell
within a period of about 5 to 15 minutes, a low rate 200 ma charger
coupled in shunt with the lead-acid battery high discharge rate
charge accumulator device and with the charger configured to
re-charge the high discharge rate charge accumulator at a low
charge rate, in comparison to the discharge rate of high discharge
rate charge accumulator and a series resistor coupled between the
accumulator and an output of the charger device.
[0010] Other aspects of the present invention are possible.
[0011] One or more of the above aspects may include one or more of
the following advantages.
[0012] The above arrangements may provide chargers at reduced costs
in comparison to conventional chargers used to fast charge
LiFePO.sub.4 batteries. For example, for LiFePO.sub.4 batteries the
power (energy delivered per unit time) required charge such
batteries to have charging accomplished within about 5 minutes to
15 minutes requires a charger having relatively expensive
components.
[0013] In addition to charging a LiFePO.sub.4 battery from an
electrical outlet, the charger incorporates an internal accumulator
that stores several charges worth of energy for a LiFePO.sub.4
battery for use in the event of a power outage. Such a supply of
reserve electrical power is stored in the charger itself (in the
accumulator) which could furnish one or more recharges to such a
LiFePO.sub.4 battery for emergency use, e.g. in the case of a
cell-phone or emergency radio powered by such a battery, or even
when powered by another type of rechargeable battery such as
conventional Li-ion, Li-Polymer, Ni--MH etc.
[0014] Other features and advantages of the invention will be
apparent from the description and from the claims.
DESCRIPTION OF THE DRAWING
[0015] FIG. 1 is a block diagram of an exemplary embodiment of a
charger with an accumulator.
[0016] FIG. 2 is a block diagram of the charger with an alternative
protection circuit.
DETAILED DESCRIPTION
[0017] Referring to FIG. 1, a relatively low cost, high rate
charger 10 for charging high-charge rate capable battery cells 20
is shown. The relatively low cost, high rate charger 10 is
configured to charge rechargeable batteries that can withstand high
currents and high charge rates, such as Li--FePO4 batteries to have
charging accomplished within about, e.g., 5-15 minutes and includes
a low cost, low charge rate charger 12 an internal rechargeable
cell or battery (termed herein an "accumulator" 14) that acts as a
fast charging interface, and which is coupled between the small,
low rate charger 12 and the external battery 20. Also included is
circuitry 16 that provides the requisite DC charging voltage at the
output of the charger 10. Circuitry 16 includes optional protection
circuitry as well as optional circuitry that reduce or steps up the
voltage, as needed, to provide the requisite output voltage from
the charger 10 to the rechargeable battery 20. One such circuit
limits inrush current into the Li--FePO4 cell, by use of a high
wattage resistor, low resistance generally in a range of about 0.05
ohms to about 0.5 ohms with 0.1 ohms being a typical value that is
placed in series, between the Pb-acid battery and the Li--FePO4
cell.
[0018] As an illustrative example, for a Li--FePO.sub.4 battery
that can be charged within about 5 minutes at an approximate rate
of 1.8 Wh/0.083 hr.=21.6W or about 6.0A a lead-acid battery is
employed. Exemplary lead acid batteries can be obtained from
Protection Tech (Protection Tech 2751 152.sup.nd Ave. Redmond Wash.
98052) in a variety of configurations and voltages, such as 2V, 4V,
6V, 8V etc. One such Pb acid battery is model UB634, a 6V, 3.4 Ah
that weighs 1.52 lbs. Another suitable model is UB445, 4V, 4.5 Ah,
1.43 lbs. These batteries are sealed, meaning that the lead acid
battery as it recharges recombines suppressed gases eliminating the
need to add water. Because the batteries are tightly sealed the
batteries will generally neither leak nor require periodic topping
off with water. Typically, two techniques are used to seal such
batteries by immobilizing the electrolyte to eliminate free-flowing
acid. One technique is the use of a gel cell, e.g., a gel such as a
silica based gel is added to the electrolyte, causing the
electrolyte to "set" in a gelatin form. The other is the use of
absorbed glass mat (AGM), in which highly absorbent glass mat
separators are used between each plate to retain the liquid
electrolyte.
[0019] Exemplary charge rates for the accumulator of C/5 to 3C (in
terms of the charge rate for the LiFePO.sub.4 battery) or (C/40 to
C/2 in terms of the accumulator) cover commonly available chargers.
Whereas the discharge rate from the accumulator would be from about
5 C to about 30 C (in terms of the LiFePO.sub.4 battery) (2.5 A to
15 A), where C is charge capacity in amp hrs.
[0020] One specific configuration for the accumulator battery is to
have the manufacturer modify a 3 cell model, such as the model
UB634 to eliminate one of the cells, providing a "2/3 UB634" model
rated at 4V, with 3.4 Ah. In this configuration the Pb acid battery
energy would be about 13.6 Wh or 7.6.times. that of the Li--FePO4
cell to be recharged. Therefore, the Pb acid cell need only be
discharged to about 13% Depth of Discharge (DOD), favoring a high
cycle life, e.g., on the order of 1,000-2,000 cycles (inference
from published data for the Hawker Energy sealed Pb-acid "D" cell)
to the LiFePO.sub.4. (Hawker P.O. Box 808 9404 Ooltewah Industrial
Drive Ooltewah, Tenn. 37363 USA). Similarly, from published Hawker
"D" cell data, it can be expect that a discharge rate of 10 A (apx.
40 W) is sustainable for 6 minutes before voltage falls below 3.6V.
Typical recharge times for the Hawker cell are about 1 hr for 100%
charge. Therefore, the modified model UB634, 4V Pb-acid battery
should be capable of delivering up to 4 Wh over a period of 6
minutes or twice the power required to fully recharge the prismatic
Li--FePO4 battery.
[0021] The charger 10 is configured to have the accumulator reach
only about 13% DOD for a single re-charge of the LiFePO.sub.4 cell.
The charger 12 is configured to allow at least about 1 hr. (or
more) to recharge the Pb-acid cell. Such a charger 10 uses a very
small charger, e.g. a 200 mA charger to recharge the accumulator. A
200 mA charger can fully recharge a 3.4 Ah Pb-acid battery in 17
hours. To "top off" the Pb-acid battery after a single Li--FePO4
recharge cycle, only about 400 mAh would be needed, which requires
just 2 hours of charging.
[0022] Other accumulator types could be employed in place of
Pb-acid such as Ni--MH, Ni--Fe etc. although on a cost basis
Pb-acid is probably most economical. A 2 cell/4V Pb-acid battery is
also convenient as it is a close match to the 3.8V usually used to
taper charge a Li--FePO4 cell. Optionally, the charger and/or the
accumulator unit can display its own "state of charge" using a
low-power LCD display that is coupled to the controllers (not
shown) in the charger 12. The display can be configured to display
the number of recharge cycles remaining available in the
accumulator 14.
[0023] Because the charger 10 provides a portable source of energy,
it may be used to recharge the Li--FePO4 battery "on the go" away
from any power outlet. When not charging a battery the charger 10
is coupled to a power outlet to re-charge the accumulator 14. While
this scheme could have a relatively larger size and weight of the
charger 10 compared to fast chargers that do not employ a Pb-acid
based internal accumulator the increased volume and weight could be
acceptable in view of the emergency power storage feature and
potential cost savings. The main cost is in the 4V Pb-acid battery,
further cost savings and size reduction might be possible by
sacrificing some battery capacity, e.g. 2.0 Ah instead of 3.4 Ah.
This should still provide for 2 fast recharge cycles and additional
1-2 slower recharges, in the event of a power outage.
[0024] The charger 10 is particularly useful for charging battery
cells of various sizes, including battery cells used in many modern
portable consumer electronic products, such as cellular telephones,
MP3 players and digital cameras. The disclosed charger 10 may be
applied to many different rechargeable battery types, including
lithium ion batteries having high rate charge capability, such as
those using lithium iron-phosphate or similar phosphate based
intercalation compounds as one of the battery electrodes. The
disclosed charger 10 may further be configured to charge different
types of batteries, including, for example, cylindrical batteries,
prismatic batteries, button-cell batteries, and so forth.
[0025] The accumulator 14 and the battery 20 are secondary cells
(or batteries). While primary electrochemical cells are meant to be
discharged, e.g., to exhaustion, only once, and then discarded,
secondary electrochemical cells can be recharged for many
times.
[0026] Referring to FIG. 2, an alternative arrangement for the
protection circuit is shown to include a circuit 22 to monitor
voltage and current conditions and an enhancement, n-type MOSFET 24
with an internal ground connection. When circuit 22 detects an
overvoltage condition it causes the MOSFET to prevent charging when
the external battery voltage reaches a set threshold, in a similar
manner as is conventionally done with Li-Ion battery packs.
OTHER EMBODIMENTS
[0027] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. For example, the charge accumulator can use
other types of high storage, fast discharge components, such as so
called "supercapacitors", i.e., "electric double-layer capacitors."
With a supercapacitor because the discharge voltage can vary based
on remaining charge it would be desirable to place a DC-DC
converter (e.g., a boost type or buck-boost type of converter at
the output of the supercapacitor prior to the rechargeable cell. In
other embodiments, the charge accumulator is a rechargeable Ni--MH
battery. Ni--Cd battery, Ni--Zn battery, Ni--Fe battery,
Ag.sub.2O--Zn battery, AgO--Zn battery, Ag.sub.2O--Cd battery,
AgO--Cd battery, Ag.sub.2O--MH battery, AgO--MH battery or a high
rate Lithium rechargeable battery such as Li--FePO.sub.4. The
charge accumulator may be physically larger and be rated to contain
substantially higher energy (W-hr) than the rechargeable battery it
is intended to recharge, to assure that the charge accumulator is
capable of recharging the rechargeable battery at a very high
rate.
[0028] Accordingly, other embodiments are within the scope of the
following claims.
* * * * *